The limiting current for reduction of ferricyanide ion at nickel: The importance of experimental conditions

Usability of alloys with different composition as electrode for electrochemical reduction of ferricyanide ion

An experimental work was performed to investigate the usability of 8 metallic alloys with different composition in electrochemical limiting diffusion current technique employing the cathodic reduction of ferricyanide. All the alloys exhibited a limiting current plateau region in their voltage–current behaviour, but not all gave a wide and smooth plateau, except one with almost pure Ni. With the alloys of including more than 50% Ni, as Ni ratio of the metal increased, smoother and wider plateau was attained, and the electrode containing 99% Ni gave the smoothest plateau. The other alloys tested can only be used as electrode in the limiting diffusion current technique in low flow velocities in which the transfer of the active ion to the electrode surface is as slow as that the mass transfer controls the rate of system.

Electrochemical removal of naphthalene from contaminated waters using carbon electrodes, and viability for environmental deployment

This work assesses the potential of electrochemical technologies for the treatment of groundwaters contaminated with petroleum hydrocarbons. Specific consideration was given to deployment in Antarctic regions where numerous fuel spills have occurred over the last two centuries, and resources and manual labour for remediation efforts are limited. The polycyclic aromatic hydrocarbon, naphthalene, was a used as a model contaminant and was treated with low-cost, active carbon electrodes to promote the active chlorine degradation pathway. Results showed that 20 mg/L naphthalene solutions could be treated to sufficient standards in less than 3 h of treatment, and that the formation of toxic and chlorinated by-products is not an issue of concern if the appropriate timeframes are used (4 h of treatment). The effects of the applied current (0-160 mA) and electrolyte concentration (0.01-0.1 M NaCl) were evaluated and a dynamic kinetic model proposed and found to be in good agreement with the experimental results. The energy consumption is an important limitation in remote environmental regions where resources are scarce. It was found that an energy usage of 104 kW h/kg of naphthalene removed could be achieved.

A method to account for the effect of hydrodynamics on polar organic compound uptake by passive samplers

Mass transfer coefficients of the water boundary layer (k_w ) were measured using alabaster dissolution kinetics in a diffusion cell that was operated at stirring rates between 90 min^-1 and 600 min^-1 , aiming to provide a more robust characterization of the effect of hydrodynamics on the uptake of polar compounds by passive samplers, as compared with characterizations in terms of stirring rates and water flow velocities. The measured k_w helped to quantitatively understand calcium sulfate transport through a poly(ethersulfone) membrane and 2 water boundary layers (at both sides of the membrane). Alabaster-based k_w value were used to understand atrazine transport in the diffusion cell, allowing the conclusion that atrazine transport in the membrane is via the pore space, rather than via the polymer matrix. The merits of measuring alabaster dissolution rates for passive sampler calibration and application in the field are discussed. The authors propose that passive sampler calibrations be carried out under controlled k_w conditions, rather than under controlled stirring rates or flow velocities. This would facilitate the interpretation of passive sampler calibration studies and the translation of laboratory-based water sampling rates to flow conditions that apply in the field. Environ Toxicol Chem 2017;36:1517-1524. © 2016 SETAC.

Influence of the Phase State of Self-Assembling Redox Mediators on their Electrochemical Activity

Self-assembling redox mediators have the potential to be broadly useful in a range of interfacial electrochemical contexts because the oxidation state and state of assembly of the mediator are closely coupled. In this paper, we report an investigation of the self-assembly of single- and double-tailed ferrocenyl amphiphiles (FTMA and BFDMA, respectively) at the surfaces of Pt electrodes and the impact of the dynamic assembled state of the amphiphiles on their rate of oxidation. We conclude that frozen aggregates of BFDMA adsorb to the surfaces of the Pt electrodes, and that slow dynamics of reorganization BFDMA within these aggregates limits the rate of electrooxidation of BFDMA. In contrast, FTMA, while forming assemblies on the surfaces of Pt electrodes, is characterized by fast reorganization dynamics and a corresponding rate of oxidation that is an order of magnitude greater than BFDMA.